AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Measuring Humidification Effects on Aerosol Optical Properties with a Novel Humidity Controlled Albedometer: Instrument Validation and Soot Experiments
TYLER CAPEK, Jared Lam, Christian Carrico, Claudio Mazzoleni, Allison Aiken, Timothy Onasch, Andrew Freedman, Manvendra Dubey, Michigan Technological University
Abstract Number: 256 Working Group: Instrumentation and Methods
Abstract A novel method for probing the single scattering albedo (SSA) of aerosol exposed to high relative humidity (RH) environments has been developed. A cavity attenuated phase-shift albedometer (CAPS PMssa) was integrated with a humidifier that allows us to control the RH of the sample volume. The CAPS PMssa uses a light source centered at 450nm, and the combined instrumentation was capable of measuring scattering, extinction, and relative humidity on the same sample volume. From these measurements, aerosol light absorption and SSA can be calculated. Optical enhancements were determined by taking the ratio of aerosol optical properties at high RH (85%) to aerosol optical properties at low RH (<20%). Light scattered by ammonium sulfate was enhanced by as much as 3.5 times. Likewise, the scattering and absorption of nigrosin was enhanced by as much as 1.5 and 1.2, respectively. Benchmark measurements of fresh soot confirm that they are hydrophobic, and do not take up water readily. The effects of aging of soot was studied by exposing it to a highly oxidative environment within an oxidation flow reactor. We detected a significant change in the single scattering albedo of the soot after aging, noting an increase from 0.3 to 0.4. We also investigated the change in the optical properties of soot exposed to humidified environments. In the future, we will focus our efforts on how the hygroscopic and optical properties of soot change when exposed to varying degrees of oxidation within the flow reactor.